The field of the present invention is laser energy delivery systems and, in particular, side firing fiber optic laser delivery systems.
Recent attention has been directed to the use of lasers in medical and dental applications. In particular, because the energy output of a laser may be precisely controlled and the thermal absorption of a given tissue area may be accurately predicted, it has been recognized by those skilled in the art that the laser provides an excellent means for causing a predictable amount of thermal damage to diseased or traumatized tissue.
It has also been recognized by those skilled in the art that optical fibers provide an excellent means for delivering laser radiation with minimal energy loss to remote tissue locations within a person's body. To this end, fiber optic laser delivery systems have been developed for use in numerous medical applications including the treatment of urological disorders, gastro-intestinal disorders, and vascular disorders. In fact, those in the medical community will recognize that fiber optic laser delivery systems may be used to deliver laser radiation to any tissue location which is accessible using a catheter, a scope, or a needle. The challenge, however, is to deliver the laser radiation to an identified tissue area in a useful and manageable form.
Conventional fiber optic laser delivery systems generally fall within one of two broad classes, contact systems and free beam systems. Contact systems, as the name suggests, utilize a contact element (i.e. an optical fiber tip or a lens element), which is placed in contact with a tissue area to be irradiated, and a beam carried by the fiber is delivered to the tissue at the point of contact. One exemplary type of contact system is the "ball tipped" system, which generally comprise an optical fiber tip having an exposed core region which is formed into the shape of a ball. In use, the ball of the fiber tip is placed in contact with the tissue to be irradiated, and substantially all of the energy delivered to the tip of the fiber is delivered to the tissue at the point of contact. It will be noted by those skilled in the art that, because the radiation passes directly from the laser fiber to the tissue to be treated, only a minimal amount of energy is lost at the tissue-fiber interface. However, because substantially all of the laser energy is delivered to the tissue at the point of contact (i.e. because substantially all of the laser energy is delivered to an extremely small tissue area), the use of contact delivery systems often results in excessive tissue vaporization and carbonization, thus making it quite difficult to treat large tissue areas in an even fashion.
Free beam laser delivery systems generally provide a means for directing a laser beam externally of a fiber toward a tissue area to be irradiated. In doing so, these systems provide a means for treating relatively large tissue areas (i.e. areas of 3-5 mm.sup.2). If a free beam delivery system emits a beam to one side of a fiber or fiber tip assembly, the system will commonly be referred to as a "side-firing" laser delivery system. Side-firing systems laser delivery systems generally comprise an optical fiber having a reflector or prism assembly mounted at one end. The reflector or prism assembly is formed and positioned to deflect a laser beam carried by the fiber to one side of the fiber.
One example of such a side-firing system is the LATERALASE system manufactured by Trimedyne, Inc., of Tustin Calif. The LATERALASE system is designed for use in conjunction with a neodymium-YAG (Nd-YAG) laser and comprises an optical fiber having an aluminum reflector assembly mounted at one end. The reflector assembly includes a gold coated reflective surface which is positioned and shaped to cause a laser beam emitted by the tip of the fiber to diverge and to be deflected to one side of the fiber. Presently, the laser beam is deflected 90.degree., but the angle of deflection may vary. Because the position and orientation of the fiber and tip assembly may be precisely controlled, the LATERALASE system may be used to cause an even and predictable amount of thermal damage to a relatively large area of tissue.
Although the LATERALASE system has been well received by the medical community, those skilled in the art will recognize that the utility of the LATERALASE system is inherently limited in two respects. First, because the gold reflective surface is not capable of total reflection of the Nd-YAG beam (the surface is roughly 98.5% reflective at the 1.06 micron wavelength), the reflective surface tends to "heat up" during use. Accordingly, as the power output of the laser is increased, the likelihood of melting the reflective gold coating increases. Once the reflective gold coating melts, continued firing of the laser may cause the reflector assembly to melt.
Another example of a side-firing laser delivery system is the TULIP system, manufactured by Intrasonix, Inc., of Burlington, Mass. In contrast to the LATERALASE system, the TULIP device utilizes a prism assembly mounted to the tip of an optical fiber to deflect a beam to the side of the fiber. Those skilled in the art will note, however, that a prism capable of bending light at a 90.degree. angle must be constructed from glass or another substance having a relatively high index of refraction, and that glasses having the required index of refraction tend to absorb energy at a wavelength of 1.06 microns (the Nd-YAG wavelength). Thus, because conventional prisms assemblies tend to absorb energy at the 1.06 micron wavelength, they too tend to retain heat during use and cannot be used to deliver a Nd-YAG laser beam at high power levels. For this reason, the TULIP system is recommended for use in the 20-40 watt power range, and has a maximum power rating of 60 watts.
It follows, based on the above discussion, that a need exists for a side-firing laser delivery system which minimizes media transition energy losses and, more importantly, a need exists for a side-firing laser delivery system which can operate efficiently at high power outputs.